Systems according to the preamble are prior art e.g. DE 20 2004 010 720 U1 and WO 2005/066058. The system comprises a movement detector, which is fitted to detect movement of the car when the machinery brake of the drive machinery is in the braking status with the purpose of holding the car in its position without moving. The movement detector forms a control signal if the car nevertheless moves undesirably in the aforementioned situation. A separate stopping appliance stops the movement of the car based on the aforementioned control signal.
The safety rules for elevators (SFS-EN 81-1 and revisions to it) give the possibility in the near future to equip an elevator with electronic safety equipment, the structural requirement for which is that it meets a certain SIL level (Safety Integrity Level) and that it incorporates a self-test function.
A problem in prior art systems for detecting and stopping uncontrolled movement is that they do not incorporate a self-test function, i.e. an inbuilt feature that detects equipment malfunction of an appliance.